The present invention relates to spin valve thin-film magnetic elements having an electrical resistance that is defined by the relationship between the fixed magnetization direction of a pinned magnetic layer and the magnetization direction of a free magnetic layer that is influenced by an external magnetic field. The present invention also relates to thin-film magnetic heads having spin valve thin-film magnetic elements. In particular, the present invention relates to a technique in which the soft magnetic characteristics of the free magnetic layer and the rate of change in resistance of a spin valve thin magnetic element is improved.
A spin valve thin-film magnetic element is a giant magnetoresistive (GMR) element having giant magnetoresistance effects. A spin valve thin film can detect magnetic fields recorded in a recording medium, such as a hard disk.
The spin valve thin-film magnetic element has a relatively simple structure among the GMR elements. Since the rate of change in resistance of a spin valve thin-film magnetic element is high in response to an external magnetic field, the spin valve thin-film magnetic element has superior characteristics in which its resistance changes in accordance with a weak magnetic field applied thereto.
FIG. 10 is a schematic cross-sectional view showing the structure of a conventional spin valve thin-film magnetic element observed from a side air bearing surface opposing a recording medium. Shield layers are formed on the upper and the lower sides of the spin valve thin-film magnetic element with gap layers disposed therebetween. The spin valve thin-film magnetic element, the gap layers, and the shield layers constitute a reproducing GMR head. In addition, on the reproducing GMR head, a recording inductive head may be provided. This GMR and inductive head on a trailing edge side portion of a floating type slider detects magnetic fields recorded in a magnetic recording medium, such as a hard disk.
The conventional spin valve thin-film magnetic element shown in FIG. 10 is a bottom type hard bias single spin valve thin-film magnetic element comprising a laminate composed of an antiferromagnetic layer 122, a pinned magnetic layer 123, a non-magnetic conductive layer 124, a free magnetic layer 125; and hard bias layers 129 positioned on the two sides of the laminate.
In this spin valve thin-film magnetic element, the moving direction of a magnetic recording medium, such as a hard disc, is in a Z direction in the figure, the direction of a leakage magnetic field is in a Y direction, and an X1 direction in the figure is a track width direction of the spin valve thin-film magnetic element.
The spin valve thin-film magnetic element shown in FIG. 10 is made of a laminate 120 having an underlying layer 121, the antiferromagnetic layer 122, the pinned magnetic layer 123, the non-magnetic conductive layer 124, the free magnetic layer 125, and a protective layer 127 layered from a bottom side in order. A pair of hard bias layers (permanent magnetic layers) 129 are positioned at the two sides of the laminate 120 and a pair of electrode layers 128 disposed on the hard bias layers 129 respectively. In general, a iron-manganese (Fexe2x80x94Mn) alloy film, a nickel-manganese (Nixe2x80x94Mn) alloy film, or a platinum-manganese (Ptxe2x80x94Mn) alloy film can be used for the antiferromagnetic layer 122. A nickel-iron (Nixe2x80x94Fe) alloy film can be used for the pinned magnetic layer 123 and the free magnetic layer 125. A copper (Cu) film can be used for the non-magnetic conductive layer 124. A cobalt-platinum (Coxe2x80x94Pt) alloy film can be used for the hard bias layers 129. A chromium (Cr) film or a tungsten (w) film can be used for the electrode layers 128. In addition, the underlying layer 121 and the protective layer 127 can be made of a tantalum (Ta) film. In this spin valve, a magnetic recording track width Tw is determined by the width of the upper surface of the laminate 120.
The magnetization of the pinned magnetic layer 123 is placed in a single domain state in the Y direction (the direction of the leakage magnetic field from the recording medium, the height direction), as shown in FIG. 10, by the exchange anisotropic magnetic field generated by the exchange coupling at the interface with the antiferromagnetic layer 122. In addition, the magnetization of the free magnetic layer 125 is aligned in a direction opposite to the X1 direction by the influence of the bias magnetic field of the hard bias layers 129. That is, the magnetization of the pinned magnetic layer 123 and the magnetization of the free magnetic layer 125 are aligned perpendicular to each other.
In this spin valve thin-film magnetic element, a sense current is applied to the pinned magnetic layer 123, the non-magnetic conductive layer 124, and the free magnetic layer 125 from the electrode layers 128 formed on the hard bias layers 129. The leakage magnetic field is applied from the magnetic recording medium. When the magnetization of the free magnetic layer 125 is changed from the direction opposite to the X1 direction to the Y direction due to the relationship of the change in magnetization direction of the free magnetic layer 125 and the fixed magnetization direction of the pinned magnetic layer 123, the electrical resistance is changed (this change is called magnetoresistance (MR) effect), whereby the leakage magnetic field from the recording medium is detected by a change in voltage in accordance with the change in electrical resistance. In the spin valve thin-film magnetic element described above, the rate of change in resistance by an applied external magnetic field is approximately 8%.
For a recording medium, such as a hard disc, a higher recording density can be required. However, to improve the recording density, the magnetic recording track width can be decreased. That is, a narrower track can be required for the spin valve thin-film magnetic element. When the magnetic recording track width Tw is decreased, the track width for detecting an external magnetic field is decreased, and hence, the change in resistance (xcex94R) by the GMR effect is decreased. Consequently, the detection sensitivity of the spin valve thin-film magnetic element is decreased, and a problem may arise in which a higher recording density is difficult to achieve. Accordingly, there is a need for a spin-valve thin film magnetic element having an 8% rate of change of resistance that has an improved detection sensitivity. In addition to the narrower track, there is a need for an improved sensitivity without increasing a gap size, i.e., without increasing the dimension in the Z direction shown in FIG. 10.
A spin valve thin-film magnetic element comprises a substrate; an antiferromagnetic layer disposed on the substrate, and a pinned magnetic layer disposed on the antiferromagnetic layer. Preferably, the magnetization direction of the pinned magnetic layer is fixed by an exchange coupling magnetic field with the antiferromagnetic layer. A non-magnetic conductive layer is positioned between the pinned magnetic layer and a free magnetic layer such that the magnetization direction of the free magnetic layer is aligned in a direction substantially perpendicular to the magnetization direction of the pinned magnetic layer. A pair of electrode layers supply a sense current to the pinned magnetic layer, the non-magnetic conductive layer, and the free magnetic layer and a bias layer to align the magnetization direction of the free magnetic layer in the direction substantially perpendicular to the magnetization direction of the pinned magnetic layer. A specular-reflection layer is positioned further from the non-magnetic conductive layer than the free magnetic layer which increases the free mean paths of conduction electrons by a specular effect. In a preferred embodiment, the film thickness of the free magnetic layer is preferably in the range of about 15 to about 45 xc3x85.
The antiferromagnetic layer preferably comprises one of an Xxe2x80x94Mn alloy and a Ptxe2x80x94Mnxe2x80x94Xxe2x80x2 alloy, in which X is one element selected from the group consisting of platinum (Pt), palladium (Pd), iridium (Ir), rhodium (Rh), ruthenium (Ru), and osmium (Os), and Xxe2x80x2 is at least one element selected from the group consisting of Pd, chromium (Cr), Ru, nickel (Ni), Ir, Rh, Os, gold (Au), silver (Ag), neon (Ne), argon (Ar), xenon (Xe), and krypton (Kr).
The specular-reflection layer preferably comprises an insulating material generating an energy gap having a high probability of producing specular reflection which conserves spin states of the conduction electrons. As the insulating material, an oxide, such as xcex1-Fe2O3, or NiO, or a half-metal Heusler alloy may be used. The film thickness of the specular-reflection layer is preferably in the range of about 10 to about 400 xc3x85, and more preferably, in the range of about 10 to about 200 xc3x85. The layers may also be disposed on a substrate in the following order, the antiferromagnetic layer, the pinned magnetic layer, the non-magnetic conductive layer, the free magnetic layer, and the specular-reflection layer.
In one preferred embodiment, the free magnetic layer and the specular-reflection layer may be separated by a back layer that preferably comprises a material selected from the group consisting of Au, Ag, and Cu. The thickness of the back layer is preferably in the range of about 5 to about 15 xc3x85.
Preferably, the pinned magnetic layer comprises a multilayer film and at least one layer of the multilayer film comprise a half-metal Heusler alloy. In addition, the half-metal Heusler alloy preferably comprises at least NiMnSb or PtMnSb, and the layer comprising the half-metal Heusler alloy may be a monolayer film or a multilayer film.
The pinned magnetic layer may comprise a first pinned magnetic layer, a second pinned magnetic layer, and a non-magnetic interlayer positioned therebetween. The first and the second pinned magnetic layers may be in a ferrimagnetic state in which the magnetization directions are about 180xc2x0 out of phase with each other.
The pair of electrode layers may be located near at least two sides of the free magnetic layer, non-magnetic conductive layer, and pinned magnetic layer in the film surface direction thereof. The pair of electrode layers may also be located further from the substrate than the antiferromagnetic layer.
Preferably, at least the antiferromagnetic layer, the pinned magnetic layer, the free magnetic layer, and the specular-reflection layer may comprise a laminate, and the pair of electrode layers is preferably provided near the two sides of the laminate. Preferably, the pair of electrode layers extend toward the laminate and are in direct contact with the free magnetic layer or back layer.
Furthermore, preferably a spin valve thin-film magnetic element comprises a substrate, an antiferromagnetic layer formed on the substrate, and a pinned magnetic layer in contact with the antiferromagnetic layer. Preferably, the magnetization direction of the pinned magnetic layer is fixed by an exchange coupling magnetic field with the antiferromagnetic layer. A non-magnetic conductive layer is preferably positioned between the pinned magnetic layer and a free magnetic layer, in which the magnetization direction of the free magnetic layer is aligned in a substantially perpendicular direction to the magnetization direction of the pinned magnetic layer. A pair of electrode layers preferably supply a sense current to the pinned magnetic layer, the non-magnetic conductive layer, the free magnetic layer, and a bias layer aligning the magnetization direction of the free magnetic layer in a substantially perpendicular direction to the magnetization direction of the pinned magnetic layer. Preferably, the pinned magnetic layer is a multilayer film, and at least one layer of the multilayer film comprises a half-metal Heusler alloy.
Preferably a thin-film magnetic head is provided with the spin valve thin-film magnetic element described above. Since the specular-reflection layer is positioned further from the non-magnetic conductive layer than the free magnetic layer, which increases the free mean paths of the conduction electrons by a specular effect, the free mean paths of the positive spin conduction electrons (spin-up conduction electrons) are increased which contributes to the magnetoresistance effect. Hence, a high rate of change in resistance (xcex94R/R) in the spin valve thin-film magnetic element can be attained. Preferably, a high recording density can be achieved.
The film thickness of the free magnetic layer is preferably in the range of about 15 to about 45 xc3x85. A free magnetic layer having a thickness of less than about 15 xc3x85 is not preferable to the preferred embodiment since the free magnetic layer is difficult to form as a soft magnetic thin-film, a sufficient magnetoresistance effect cannot be obtained, and in addition, the rate of change in resistance is decreased due to the presence of conduction electrons which perform diffusive scattering and no specular reflection described later.
In addition, a free magnetic layer having a thickness of more than about 45 xc3x85 is also not preferable since spin-up conduction electrons are increased which are scattered before reaching the specular-reflection layer, and hence, the ratio of the rate of change in resistance improved by the specula effect is decreased.
In the spin valve thin-film magnetic element described above, the antiferromagnetic layer may comprise an alloy comprised of manganese (Mn) and at least one element selected from the group consisting of Pt, Pd, Rh, Ru, Ir, Os, Au, Ag, Cr, Ni, Ne, Ar, Xe, and Kr, or may comprise an alloy represented by the formula Xxe2x80x94Mn in which X is one element selected from the group consisting of Pt, Pd, Ru, Ir, Rh, and Os, and in which X is preferably in the range of about 37 to about 63 atomic percent. In addition, in the spin valve thin-film magnetic element described above, the antiferromagnetic layer may comprise an alloy represented by the formula Ptxe2x80x94Mnxe2x80x94Xxe2x80x2 in which Xxe2x80x2 is at least one element selected from the group consisting of Pd, Cr, Ru, Ni, Ir, Rh, Os, Au, Ag, Ne, Ar, Xe, and Kr, and in which Xxe2x80x2+Pt is preferably in the rage of about 37 to about 63 atomic percent.
Accordingly, when an antiferromagnetic layer is used which comprises an alloy represented by the formula Xxe2x80x94Mn or an alloy represented by the formula Ptxe2x80x94Mnxe2x80x94Xxe2x80x2, compared to a spin valve thin-film magnetic element having an antiferromagnetic layer composed of a NiO alloy, a Fexe2x80x94Mn alloy, a Nixe2x80x94Mn alloy, or the like, a spin valve thin-film magnetic element can be produced having superior characteristics, such as a strong exchange coupling magnetic field, a high blocking temperature, and a superior corrosion resistance. Since the preferred specular-reflection layer comprises an insulating material generating an energy gap having a high probability of producing specular reflection which conserves spin states of conduction electrons, the rate of change in resistance can be improved by the specular effect described later.
As an insulating material forming the specular-reflection layer described above, there may be oxides, such as xcex1-Fe2O3, NiO, CoO, Coxe2x80x94Fexe2x80x94O, Coxe2x80x94Fexe2x80x94Nixe2x80x94O, Al2O3, Alxe2x80x94Qxe2x80x94O in which Q is at least one element selected from the group consisting of boron (B), silicon (Si), nitrogen (N), titanium (Ti), vanadium (V), Cr, Mn, iron (Fe), cobalt (Co), and Ni, and Rxe2x80x94O in which R is at least one element selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W; nitrides, such as Alxe2x80x94N, Alxe2x80x94Qxe2x80x94N in which Q is at least one element selected from the group consisting of B, Si, O, Ti, V, Cr, Mn, Fe, Co, and Ni, and Rxe2x80x94N in which R is at least one element selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W; and the like.
When an antiferromagnetic material, such as xcex1-Fe2O3 or NiO, is used as the specular-reflection layer, the specular-reflection layer may also be used as the whole bias layer or a part thereof.
As an insulating material for forming the specular-reflection layer, a half-metal Heusler alloy may also be used, and the specular-reflection layer may be a monolayer or a multilayer comprised of a half-metal Heusler alloy comprising at least one of NiMnSb and PtMnSb. When these materials are used, a sufficient potential barrier between the specular-reflection layer and a layer adjacent thereto can be formed, and as a result, a sufficient specular effect can be obtained. In addition, the film thickness of the specular-reflection layer is preferably in the range of about 10 to about 400 xc3x85, and more preferably, in the range of about 10 to about 200 xc3x85.
A specular-reflection layer having a thickness of less than about 10 xc3x85 is not preferable since a continuous and uniform oxide film having a crystalline structure capable of forming a potential barrier cannot be obtained. As a result, the detection sensitivity is decreased, and hence, the reproducing output characteristics of the spin valve thin-film magnetic element are degraded.
In addition, a specular-reflection layer having a thickness of more than about 400 xc3x85 is not preferable since the specular-reflection layer serves as an antiferromagnetic layer, and as a result, an unexpected exchange coupling magnetic field (Hex) may be generated. Furthermore, when a thin-film magnetic head is formed, it is not preferable since the shield distance, i.e., a reproducing gap, is excessively increased, and as a result, the resolution of the head is degraded.
Since the back layer comprised of a non-magnetic conductive material selected from the group consisting of Au, Ag, and Cu is provided between the free magnetic layer and the specular-reflection layer, the mean free paths of positive spin (spin-up) conduction electrons are increased which contribute to the magnetoresistance effect. Consequently, a high rate of change in resistance (xcex94R/R) can be obtained in the spin valve thin-film magnetic element by a spin filter effect, and hence, a high recording density can be achieved.
The film thickness of the back layer is preferably in the range of about 5 to about 30 xc3x85, and more preferably, in the range of about 5 to about 15 xc3x85. A back layer having a thickness of less than about 5 xc3x85 is not preferable since the effect of increasing the free mean paths of positive (+) spin electrons is decreased. That is, the spin filter effect is decreased.
In addition, a back layer having a thickness of more than about 30 xc3x85 is not preferable since the ratio of a sense current shunting to the back layer composed of a non-magnetic conductive material is increased. Hence, a sense current flowing in the vicinity of the interface of the free magnetic layer and the non-magnetic conductive layer is decreased which can be needed for obtaining the GMR effect. That is, due to an increase in shunt loss, a high rate of change in resistance (xcex94R/R) is difficult to obtain.
Since the pinned magnetic layer is preferably comprised of a multilayer film, and at least one layer thereof is a monolayer or a multilayer comprised of a half-metal Heusler alloy comprising at least one of NiMnSb and PtMnSb, a specular effect can be obtained in a part of the pinned magnetic layer as is the case of the specular-reflection layer. Consequently, a higher rate of change in resistance (xcex94R/R) can be obtained in the spin valve thin-film magnetic element by an increase in free mean paths of the conduction electrons.
Since a ferromagnetic half-metal alloy, such as NiMnSb, or PtMnSb, is disposed between an upper and a lower ferromagnetic layer comprising the pinned magnetic layer, the magnetizations of the ferromagnetic layers in the vertical direction are in the same direction, the multilayer film behaves as if a monolayer film does although the multilayer film is actually a three-layered structure. Hence, stable magnetic characteristics can be obtained. Accordingly, a specular effect can be obtained in the state described above, and as a result, the rate of change in resistance can be improved.
In addition, a synthetic-ferri-pinned type spin valve thin-film magnetic element may be formed in which the pinned magnetic layer is formed of a first pinned magnetic layer and a second pinned magnetic layer with a non-magnetic interlayer provided therebetween and in which the magnetization directions of the first and the second pinned magnetic layers are antiparallel to each other so that the pinned magnetic layer is placed in a ferrimagnetic state. Accordingly, the exchange coupling magnetic field (an exchange anisotropic magnetic field) Hex generated at the interface of the antiferromagnetic layer and the first pinned magnetic layer can be increased. One of the first and the second pinned magnetic layers serves to fix the magnetization of the other pinned magnetic layer in an appropriate direction, and hence, the entire pinned magnetic layer is conserved in a very stable state.
In addition, when a spin valve thin-film magnetic element is formed having a pinned magnetic layer comprised of a first and a second pinned magnetic layers with a non-magnetic interlayer provided therebetween, the magnetostatic coupling fields of the first and the second pinned magnetic layers can counteract the demagnetizing field (the dipole magnetic field) by the fixed magnetization of the pinned magnetic layer. Accordingly, the influence of the demagnetizing field, generated by the fixed magnetization of the pinned magnetic layer, to the direction of the rotatable magnetization of the free magnetic layer can be decreased. Preferably, a layer comprised of the half-metal Heusler alloy described above may be provided at the non-magnetic conductive layer side than the non-magnetic interlayer. That is, the layer described above may be provided in contact with the second pinned magnetic layer or may be provided therein. As a result, a specular effect can be additionally obtained at a side further from the specular-reflection layer than the free magnetic layer. Hence, the rate of change in resistance can be increased.
The pair of electrode layers may be provided at least two sides of the free magnetic layer, the non-magnetic conductive layer, and the pinned magnetic layer in the film surface direction and may be disposed further from the substrate than the antiferromagnetic layer. As a result, the ratio of a sense current supplied in the vicinity of the free magnetic layer exhibiting the GMR effect can be increased without flowing through the antiferromagnetic layer and the bias layer, which have higher resistances compared to the free magnetic layer and the non-magnetic conductive layer. Hence, the rate of change in magnetic resistance in the spin valve thin-film magnetic element can be improved.
In addition, since a sense current can be supplied in the vicinity of the free magnetic layer from the electrode layers while conserving the single domain state of the free magnetic layer, side reading can be prevented, and a higher magnetic recording density can be more effectively achieved.
The principle of the giant magnetoresistance effect in the spin valve thin-film magnetic element will be described briefly. For the purposes of this description, the back layer and the specular-reflection layer are not in contact with the non-magnetic conductive layer adjacent to the free magnetic layer.
When a sense current is supplied to the spin valve thin-film magnetic element, conduction electrons can primarily move in the vicinity of the non-magnetic conductive layer having a low electrical resistance. In conduction electrons, it is highly probable that a substantially equal number of spin-up conduction electrons and spin-down conduction electrons are present.
The rate of change in magnetic resistance in the spin valve thin-film magnetic element has a positive relationship with the difference in free mean path between these two types of conduction electrons.
The spin-down conduction electrons are generally diffused at the interface of the non-magnetic conductive layer and the free magnetic layer regardless of the direction of an applied external magnetic field. The probability of moving into the free magnetic layer is maintained at a lower level, and the free mean paths of the spin-down conduction electrons are relatively short compared to those of the spin-up conduction electrons.
On the other hand, the spin-up conduction electrons have a higher probability of moving from the non-magnetic conductive layer to the free magnetic layer when the magnetization directions of the free magnetic layer and the pinned magnetic layer are parallel to each other by an external magnetic field. Hence, the free mean paths are increased. In addition, as the magnetization direction of the free magnetic layer rotates by an external magnetic field from a direction parallel to the magnetization of the pinned magnetic layer, the probability of scattering at the interface of the non-magnetic conductive layer and the free magnetic layer is increased. As a result, the free mean paths of the spin-up conduction electrons are decreased.
As described, by an application of an external magnetic field, the free mean paths of the spin-up conduction electrons can be changed compared to those of the spin-down conduction electrons. As a result, the difference in the free mean path therebetween is significantly changed. Accordingly, the resistivity is changed, and the rate of change in magnetic resistance (xcex94R/R) of the spin valve thin-film magnetic element is increased.
When the back layer is connected to the free magnetic layer, the spin-up conduction electrons moving in the free magnetic layer can move into the back layer, and the free mean paths of the spin-up conduction electrons can be increased in proportion to the thickness of the back layer. Accordingly, a spin filter effect can be obtained, the difference in free mean path between the conduction electrons is increased, and the rate of change in magnetic resistance (xcex94R/R) in the spin valve thin-film magnetic element can be improved.
In addition, when the specular-reflection layer is formed not in contact with the non-magnetic conductive layer adjacent to the free magnetic layer, the specular-reflection layer forms a potential barrier at the interface with the free magnetic layer and can reflect the spin-up conduction electrons moving in the free magnetic layer while conserving the spin states. Accordingly, the free mean paths of the spin-up conduction electrons can be increased, that is, a specular effect can be obtained. As a result, the difference in free mean path between the spin dependent conduction electrons is increased, and hence, the rate of change in magnetic resistance in the spin valve thin-film magnetic element is improved.
Furthermore, when the specular-reflection layer is formed on the surface opposite to the free magnetic layer of the back layer, the spin filter effect and the specular effect can be obtained simultaneously, and hence, the free mean paths of the spin-up conduction electrons can be increased. That is, the difference in free mean path between the spin dependent conduction electrons can be increased, and the rate of change in magnetic resistance can be improved.
The difference of the free mean paths by the back layer and the specular-reflection layer can be obtained when the free magnetic layer is relatively thin, and simultaneously, by controlling the film thicknesses of the layers that increase the free mean paths, the magnetization of the free magnetic layer is controlled. Hence, detection sensitivity and output characteristics of a spin valve thin-film magnetic element having a narrower track can be improved.
The spin valve thin-film magnetic element may comprise a bottom type single spin valve formed in the following order and comprising at least an antiferromagnetic layer, a pinned magnetic layer, a non-magnetic conductive layer, a free magnetic layer, and a vertical bias layer on a substrate side or surface. Alternatively, the spin valve thin-film magnetic element may comprise a top type single spin valve formed in the following order and comprise at least a vertical bias layer, a free magnetic layer, a non-magnetic conductive layer, a pinned magnetic layer, and an antiferromagnetic layer on a substrate or surface.
In addition, when a spin valve thin-film magnetic element is comprised of a free magnetic layer comprised of two films with a non-magnetic interlayer provided therebetween, the exchange coupling magnetic field is preferably generated between the two films comprising the free magnetic layer. Preferably, the free magnetic layer is in a ferrimagnetic state, and the magnetization direction of the free magnetic layer rotates in response to an external magnetic field.